You have to deal with these people from what they understand. These types of people don’t think about threatening letters like you and I. They believe that they have a right to warn off bad neighbors that will threaten their property. My letter will first alert them that I am aware of their harassment, and then assure them that as the owner of the property you have a goal to rent to the best tenant possible. You will be following your leasing process which includes assessing the prospective tenant’s ability to pay as well as their character. While you can’t be held accountable for their actual character, you do have an interest in making sure the tenant passes some standards during background checks. If they allow you to use your tenant selection process it will reduce the time and also prevent you from having to report them to police send them lawyers, blah, blah, blah, etc., etc., etc.
I had a different problem. About 3 years ago, I had a guy that believed that he owned one of my properties (his grandmother owned it about 3 owners ago). When I would put up for rent signs, he would take them down. When perspective tenants would come by, he would tell them that he was the owner and the property was not for rent. I sent the police to see him, I had my lawyer threaten to sue him (but he owned nothing). I had to take matters into my own hands. I started to show the property to prospective tenants myself instead of having them just drive by and walk the property. Me being there, I was a deterrent. The only thing that really worked for that situation is that he turned up dead one day.